alarmtimer: Ensure RTC module is not unloaded

alarmtimer: Ensure RTC module is not unloaded

When registering the rtc device to be used to handle alarm timers,
get_device is used to ensure the device doesn't go away but the module can
still be unloaded.

Call try_module_get to ensure the rtc driver will not go away.

Reported-and-tested-by: Michal Simek <[email protected]>
Signed-off-by: Alexandre Belloni <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Acked-by: John Stultz <[email protected]>
Cc: Stephen Boyd <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]